Present offset printing machines have two different types of delivery. In one case, the printed sheets are guided and dropped in a receiving shelf adjacent the delivery end of the machine. In the other case, a cylinder disposed adjacent the delivery end and equipped with sheet gripping members transfers each sheet to a series of similar gripping elements which are mounted on chains and carry the sheets to a tray located at some distance from the machine.
In number of cases, such as for invoice sheet printing, it is necessary to imprint consecutive numbers on successive sheets being fed through the duplicating machine. At present, there does not exist a separate attachment device which may be added to already existing machines so that the sheets may be numbered consecutively. Distinct numbering devices are built for each type of duplicating machines. On duplicating machines having a chain type delivery, the numbering device is located in the chain delivery attachment itself; hence, should repair or change of the numbering device be required, the whole chain delivery attachment must be removed and replaced. On the other type of offset machine, the numbering device is built in the machine and, should repair or replacement be required, the printing machine cannot even be used for normal printing.